There exist currently many types of motorized or engine-driven propulsion systems for boats and other marine vehicles or vessels (collectively referred to herein generally as “marine vessels”). An inboard engine marine propulsion system for example typically involves an engine that is situated (and supported) within the body (or hull) of the marine vessel and that drives a crankshaft that in turn, by way of one or more connections, drives one or more propellers situated along the exterior of the hull of the marine vessel (often at the rear of the vessel). In such a design, the connections between the propellers and the engine are all situated within the hull of the marine vessel, and the propellers are typically fixed in their axial orientation relative to the hull. An additional form of marine propulsion system that can be considered a variant of the inboard engine marine propulsion system is a “jet boat” marine propulsion system, where instead of employing propellers along the exterior of the marine vessel, water rather is drawn into tunnel(s) extending through hull and then pumped outward from those tunnels to propel the vessel.
Further for example, a pod-type marine propulsion system also employs power provided by an engine situated internally within the body (hull) of the marine vessel. However, rather than having propeller(s) axially fixed in relation to the hull, the propeller(s) in such a system are mounted on a pod structure extending downward beneath the hull, and power is transmitted from the engine within the hull down beneath the hull through the pod structure and ultimately to the propeller(s) located thereon. Because a pod structure employed in a marine vessel having a pod-type marine propulsion system is typically rotatable about a steering (vertical or substantially-vertical) axis of the marine vessel, such a marine vessel employing a pod-type marine propulsion system typically has enhanced maneuverability relative to marine vessels employing standard inboard engine marine propulsion systems with axially-fixed propellers.
While all of the above-described types of marine propulsion systems have their merits and are well-suited for respective marine vessel applications, each of those systems can be disadvantageous in certain respects. In particular, in such systems, typically a number of components such as the propeller(s) remain continually in the water even when the marine vessel is not in active use. Consequently, such systems often utilize expensive components that are designed to withstand near-constant exposure to water. Relatedly, some components of such systems can be difficult to service due to their being within the water or otherwise difficult to access.
Further, such systems typically are lacking in maneuverability to some extent. As already discussed, standard inboard engine marine propulsion systems with axially-fixed propellers typically allow for less maneuverable than pod-type marine propulsion system in terms of steering maneuverability, particularly since axially-fixed propellers do not generally allow for adjustments in the direction of thrust about a steering (vertical or substantially-vertical) axis of the marine vessel. Yet all of these conventional systems are further lacking in terms of the ability to adjust the thrust direction up or down about an additional trimming axis that can be understood as a horizontal (or substantially horizontal) axis perpendicular to both the steering (vertical or substantially vertical) axis of the marine vessel and the front-to-rear (bow-to-stern) axis of the marine vessel. This can be problematic particularly for marine vessels that vary considerably in their speeds. Many marine vessel hulls are designed so that, as the marine vessel varies in speed, the angle of attack of the hull (that is, an inclination of the hull) relative to the water line changes. In such marine vessels, to the extent that the propulsion systems fail to allow for thrust adjustments about the trimming axes of the marine vessels, the effectiveness of the propulsion systems in propelling the marine vessels forward through the water varies and can decline depending upon the marine vessels' speeds and changing angles of attack.
A further variant of marine propulsion system that can address some of these problems is the sterndrive marine propulsion system. In such a system, like those already described, an engine is supported within the body (hull) of the marine vessel. However, rather than employing fixed propeller(s) or pump(s) or the above-discussed steerable pod of a pod-type marine propulsion system, an additional outboard assembly including one or more propellers is mounted at (so as to extend from) the stern of the marine vessel. Thus, the driving apparatus of the marine vessel is separated into two primary parts, the engine within the hull of the vessel and the additional outboard assembly with the propeller(s) and associated componentry.
In such a sterndrive marine propulsion system, although the outboard assembly is connected by way of one or more linkages to the output of the engine so that rotational power from the engine can be received at the outboard assembly and ultimately communicated to the propeller(s) of the outboard assembly, the outboard assembly is mounted to the marine vessel in a rotatable manner such that the outboard assembly can not only be steered relative to the marine vessel about a steering axis but also can be rotated about a trimming axis (again substantially perpendicular to both the steering axis and the front-to-rear axis of the marine vessel, where substantially perpendicular can occur, for example, when at zero trim). By virtue of this, the sterndrive marine propulsion system not only allows for good steering maneuverability but also allows for adjustment of the thrust direction about the trimming axis so as to enhance the effectiveness of the propulsion system in driving the marine vessel. Further, rotation of the outboard assembly about the trimming axis can allow for removal of the propeller(s) out of the water when not being used, such that those components need not be designed to withstand as much wear-and-tear from exposure to the elements, and also are easier to access for servicing.
Although sterndrive marine propulsion systems can be advantageous in the above respects, such marine propulsion systems along with the other inboard engine marine propulsion systems already discussed share in common the disadvantage that, by situating the engine within the hull of the marine vessel, valuable space within the main body of the marine vessel is taken up. This is often disadvantageous since space within a marine vessel is often at a premium and would preferably be utilized for other purposes such as for cabin space, storage, etc. Further, the effectiveness of a propulsion system in propelling a marine vessel forward can often be enhanced if the marine vessel's angle of attack is inclined as the marine vessel planes through the water. Yet placement of an engine of a marine vessel within the hull of the vessel, as is the case in all of the aforementioned types of marine propulsion systems, tends to counteract this effect. This is because the engine is often the heaviest, or one of the heaviest, portions of a marine vessel, and consequently placement of the engine within the hull tends to reduce the marine vessel's angle of attack (or work against further increases in that angle of attack).
Yet a further type of marine propulsion system, namely, the outboard motor marine propulsion system, addresses some of the aforementioned disadvantages. Like sterndrive marine propulsion systems, outboard motor marine propulsion systems include an outboard assembly that is rotatably mounted at the stern of the marine vessel with which it is associated in a manner such that the outboard assembly can be rotated both about a steering axis and a trimming axis. Thus, outboard motor marine propulsion systems not only offer maneuverability in terms of steering but also offer the advantages described above with respect to sterndrive marine propulsion systems in terms of achieving enhanced propelling of the boat notwithstanding changes in the angle of attack of the marine vessel, reducing the need for specialized components capable of withstanding the elements, and facilitating servicing.
Additionally, in contrast with sterndrive marine propulsion systems, the motor or engine of an outboard motor marine propulsion system is also located on the outboard assembly itself rather than within the hull of the marine vessel. Such placement of the engine allows for the aforementioned disadvantages associated with inboard engine placement to be overcome. In particular, valuable space within the hull no longer needs to be allocated to the engine, thus freeing up that space for other uses. Also, since the weight of the engine is placed at (so as to extend behind) the stern of the marine vessel as part of the outboard assembly, the angle of attack of the marine vessel tends to be further increased rather than diminished by the engine placement, thus resulting in better powering of the marine vessel.
Outboard motor marine propulsion systems also allow for additional advantages to be achieved as well. For example, for various reasons, the engines employed in outboard motor marine propulsion systems often can be more efficient in design and lower in weight than inboard engines providing the same amount of drive power. Additionally, because the engine/motor is integrated within the outboard assembly in an outboard motor marine propulsion system such systems tend to be robust, and removal of the entire (or substantially the entire) driving apparatus of the marine vessel can be easily achieved to not only facilitate servicing of the components of that driving apparatus but also facilitate transporting of the driving apparatus (as well as the marine vessel, either in combination with the driving apparatus or separate therefrom), storage of the driving apparatus, and replacement of the driving apparatus with another driving apparatus.
Given the above advantages associated with outboard motor marine propulsion systems, in many respects these propulsion systems are the most effective marine propulsion systems available for a wide variety of marine vessel applications. Even so, conventional outboard motor marine propulsion systems are disadvantageous in one or more respects. Above all, there exists an ongoing demand for larger and more powerful marine vessel propulsion systems, so as to increase the speed and agility of marine vessels and the ease of use and excitement associated with operating marine vessels. This demand is further heightened by the growth in size and weight of marine vessels themselves, particularly yachts and other pleasure craft. Yet conventional outboard motors are limited in terms of the power that the motors can generate and deliver to the propeller(s) of the outboard motors for driving marine vessels. Indeed conventional outboard motors have topped out, in terms of the maximum power output from a single motor, at around 350 horsepower, and improvements in power output to get to even that level have been difficult to achieve.
Although in some marine vessel applications these problems have been at least partly overcome by mounting multiple (often, for example, three or four) outboard motors on a single marine vessel so as to achieve a larger combined power, such efforts have only met with limited success. Not only can the implementation and control of multiple outboard motors be a costly and complicated, but also the use of multiple outboard motors is a rather inefficient manner of achieving higher power for a marine vessel. While each additional outboard motor added to a marine vessel increases the overall driving power available for the marine vessel, the amount of increased driving power is not as large as might be hoped for because, in addition to outputting power, each additional outboard motor also increases the drag affecting movement of the marine vessel due to the interaction between that assembly and the water into which that assembly descends.
For at least these reasons, therefore, it would be advantageous if an additional new or improved marine propulsion system could be developed that, in at least some embodiments, would achieve one or more of the above-described advantages associated with existing outboard motor marine propulsion systems and yet also would overcome entirely, or to a significant degree, the aforementioned disadvantages associated with the use of conventional outboard motors, and/or would achieve one or more other advantages. Among other things, it would be desirable if a new or improved outboard motor marine propulsion system could be developed that, in at least some embodiments, allowed for the output of substantially greater power levels than conventional outboard motor marine propulsion systems, or otherwise allowed for one or more enhanced manners of operation or implementation of an outboard motor marine propulsion system.